This invention relates to clay-based compositions suitable for the purification of edible oils. In particular, the present invention is directed to clay and organic acid compositions useful in the pretreatment of edible oils prior to bleaching.
Fats and fatty oils, commonly called triglycerides, are triesters of glycerol, and include minor amounts of fatty acids. At ambient temperatures of about 20 to about 25 degrees C fats are solids, whereas fatty oils are liquids.
Triglycerides are widely distributed in nature. Some triglycerides are edible while others are not. Many are derived directly from vegetable, animal, and marine sources. Others are obtained, as by-products, in the production of fiber from vegetable matter, and in the production of protein from vegetable, animal or marine matter.
Edible vegetable oils include canola, coconut, corn germ, cottonseed, olive, palm, peanut, rapeseed, safflower, sesame seed, soybean, and sunflower oils. Examples of nonedible vegetable oils are jojoba oil, linseed oil and castor oil.
Illustrative sources of edible animal-derived oil include lard and tallow. Examples of nonedible animal-derived oil are low grade tallow and neat""s-foot oils.
Crude edible oils contain a number of impurities, both naturally occurring and introduced in storage and processing, that must be removed. Such impurities include phospholipids, soaps, phosphorus, and trace metals, including calcium, magnesium, iron and copper. See generally, Jamieson, G. S. Vegetable Fats and Oils, Reinhold Publishing Corp., New York (1943).
Phospholipids, which occur in most natural fats and oils include lecithin, cephalin (phosphatidylethanolamine) and phosphatidylinositol. Phospholipids can cause objectionable colors, odors and flavors in a finished oil product.
Phosphorus and metal ions such as calcium, magnesium, iron, and copper are believed to be chemically associated with phospholipids, including phosphatides, have deleterious effects on refined oil products. Moreover, calcium and copper can form precipitates, while iron and copper promote oxidative instability. Each metal ion is associated with catalyst poisoning where refined oil is catalytically hydrogenated at a later step.
Free fatty acids (FFA) result from hydrolysis of the triglycerides of the edible oils. Color impurities typically present in oils include, for example, carotenoids, xanthophylls, xanthophyll esters, chlorophyll, tocopherols, as well as oxidized fatty acids and fatty acid polymers. Peroxides (reported as peroxide value, PV) are products of oxidation of the oil.
Edible oils are generally subjected to a number of processing steps. The usual treatment steps are shown in FIG. 1 which is provided as a general summary. Some processing methods may omit some of these steps, while other steps may be required in some applications. See generally Swoboda, P. A. T., J. Amer. Oil Chem. Soc. 62: 287-292 (1985). The present invention relates especially to the steps up to and including clay bleaching.
Crude edible oil from storage is subjected to degumming, which comprises treatment with an acid such as phosphoric or citric acid. Degumming prepares the phosphatides for removal. Following degumming the oil may be physically refined, chemically refined or both. Refining removes the bulk of the phosphatides, primarily as calcium and magnesium salts. Physical refining comprises exposing the oil to steam so as to remove undesirable constituents. Chemical refining involves neutralization of the acid-degummed oil with alkali followed by water washing and centrifugation. Neutralization of the oil with alkali can produce soaps that must be removed at later steps.
A sorptive purification step prior to bleaching further removes impurities from the oil before it contacts the bleaching clays. This pretreatment of the oil before the bleaching step removes substantial amounts of impurities remaining from the previous steps, thereby improving the efficiency and useful life of the bleaching clays.
Clay bleaching also removes colors that might be objectionable to a consumer. Bleaching clays generally improve oil color quality by adsorbing color impurities that are present.
The use of a clay pre-treatment sorbent for sorptive purification provides several benefits to the refiner. By removing most of the contaminants upstream, the efficacy of the bleaching clay is improved significantly. The absence of contaminants prevents xe2x80x9cpoisoningxe2x80x9d of the bleaching clay and leaves more active sites exposed on the clay surface to adsorb chlorophyll and color bodies. Improved efficiency of the bleaching clay also means that the refiner can reduce the total amount of clay while achieving a better final product. Reduced clay dosages, in turn, reduce spent filter cake disposal.
What is needed as such a pre-treatment product is a filtering sorbent medium which has a high affinity for polar contaminants such as phospholipids, soaps, and trace metals from glyceride oils prior to bleaching. By removing most of such contaminants upstream, the efficacy of the bleaching clay is improved significantly. The clays used in the present invention have more than twice the porosity of other commercially available clays.
We have found that the addition of certain dry granular organic acids to high porosity clay greatly enhances its adsorption capabilities for these polar contaminants which capabilities meet or exceed the performance of commercially available silica gels.
Such a pre-treatment sorbent clay product provides several economical and environmental benefits. Improved efficiency of the bleaching clay would permit a reduction in the total amount of clay (pre-treatment sorbent plus bleaching clay) while achieving a better final oil product. Effective removal of soaps allows the elimination of the water wash processing step, which is costly and currently has a number of environmental implications due to the need for proper disposal of the waste water.
Highly active clay-derived pre-treatment sorbents are obtained by the co-grinding of clays with dry, granular organic acids having a pKa value in the range of about 1 to about 7 and being substantially free from organic acid salts. The pre-treatment clay adsorbents of the present invention improve the efficiency and useful life of bleaching clays. The pre-treatment clay sorbents also are environmentally responsible alternatives to silica gels, thereby reducing the total clay used in the process and eliminating a wash step that produces waste water.
Clay combined with anhydrous malic acid or the like organic acid produces a highly active pre-treat sorbent capable of removing polar contaminants from refined glyceride oils such as soybean and canola when used in a sorptive purification step that precedes bleaching. Such contaminants include soaps, phospholipids and associated trace metal ions (magnesium, calcium, iron, and copper) which, when present at certain levels in oil, have a deleterious effect on taste, odor, color, and stability. The pre-treatment sorbent of the present invention provides performance comparable to that of silica gel adsorbents in the removal of phospholipids and trace metals, as well as in soap removal. The present pre-treatment sorbent composition also provides a number of additional advantages over silica gels such as improved bleaching of red colors, effective chlorophyll removal, and reduction of peroxide values. The stability of the pre-treatment sorbent composition is excellent at moisture levels below about 5 weight percent.